This invention relates to sealing an open end parison at orientation temperature.
The blow molding art goes back over 100 years. Traditionally, blow molded articles have been formed by the downward extrusion of a molten parison from an annular die into position between opposing mold halves. The mold halves are then closed and fluid pressure introduced into the parison to expand same into conformity with the mold. Recently, techniques have been developed whereby high strength articles having exceptional sparkle and clarity can be produced by blow molding a parison preform which has been cooled to room temperature and thereafter reheated to orientation temperature so as to achieve molecular orientation in the resulting article during the fabrication steps. It is apparent that the most economical manner to produce individual parison preforms is to extrude a continuous length of tubular material and thereafter sever it into individual work pieces, as opposed to injection molding a closed end parison preform, for instance. However, this preferred method of forming individual parison preforms carries with it the inherent disadvantage of providing a preform which is open at each end and which, therefore, must be closed at one end preparatory to blow molding. Thus, in order to operate economically with individual parison preforms, the artisan is faced with the problem of achieving a seal in a parison which is at orientation temperature and thus far below the temperature at which the parison would be tacky and easily sealable. Such preforms can be sealed with fair reliability by the application of extremely high pressure from a plurality of directions radially inward toward a point while simultaneously pressing downward on the thus closed end, but this involves the use of complex equipment and increases the cycle time.